GNGTS 2021 - Atti del 39° Convegno Nazionale

57 GNGTS 2021 S essione 1.1 SEISMOGENIC STRUCTURES ORIENTATIONAND STRESS FIELD OF THE GARGANO PROMONTORY (SOUTHERN ITALY) FROM MICROSEISMICITY ANALYSIS S. Miccolis 1 , M. Filippucci 1 , S. de Lorenzo 1 , A. Frepoli 2 , P. Pierri 1 , A. Tallarico 1 1 Dipartimento di Scienze della Terra e Geoambientali, Università degli Studi di Bari Aldo Moro, Bari, Italia 2 Osservatorio Nazionale Terremoti (ONT), Istituto Nazionale di Geofisica e Vulcanologia (INGV), Rome, Italia Historical seismic catalogs report that the Gargano Promontory (southern Italy) was affected in the past by earthquakes with medium to high estimated magnitude. The instrumental seismicity showed that the most energetic Apulian sequence occurred in 1995 and consisted of a main shock of MW = 5.2 followed by ca. 200 aftershocks of magnitude lower than 3.7. The most energetic earthquakes, originally associated to right-lateral strike-slip faults, were newly attributed to the thrust or thrust-strike faults. The current work shows a detailed study on focal mechanisms and stress field obtained by micro-seismicity of Gargano area from April 2013 until the present time. Seismic waveforms were collected from OTRIONS Seismic Network (OSN) and Italian National Seismic Network (RSN). When possible, these data were integrated with those ones recorder by Italian National Accelerometric Network (RAN) to realize a robust dataset of earthquake localizations and focal mechanisms. The database used is composed of 635 well-located earthquakes (Fig. 1A) with estimated magnitude lower than 2.0 (Mlv, from April 2013 until December 2018 and Ml from January 2019) for the 90% of the events. The data show a dense and sparse seismic activity along the whole Gargano Promontory that is not related to any seismic sequence. The recorded seismicity is distributed along a NE-SW direction with the deepest events located in the NE sector. Furthermore, a seismicity peak can be observed at depths ranging between 18 km – 27 km (Fig. 1B) Focal mechanisms were computed by selecting 200 earthquakes characterized by a minimum of six P-wave polarities data, which were processed with the FocMec code (Snoke et al ., 1984). Then, in order to select the preferred fault planes among the inferred solutions, we used the approach described by Hardebeck and Shearer (2002) finding out a total of 36 well-constrained focal mechanisms that were subsequently used to compute the stress tensor inversion. Fig. 1